In the related art, starting power-generating systems having a starter generator, which functions as a starter motor at the time of starting an engine and that functions as a generator and charges a battery after the engine is started, are known (for example, refer to Patent Document 1). A motor in which the generator and the starter motor are integrated in this way may be referred to as an alternating current generator (ACG) starter. The ACG starter is installed coaxially with, for example, a crankshaft that is a rotation output shaft of the engine, and a rotor is coupled to the crankshaft. By using the ACG starter, the need for including a related-art cell motor type starter disappears. For this reason, weight and costs can be reduced, and generation of noise caused by a reduction gear that couples the cell motor type starter and the crankshaft together can be eliminated. Additionally, in vehicles that perform idling stop, which have recently been become more common, the ACG starter is preferably used.